For example, a thermal-type flow rate sensor described in JP-B2-3328547 detects a flow rate of a fluid by utilizing the fact that heat caused by a heater is robbed by the fluid passing the vicinity of the heater.
The thermal-type flow rate sensor in JP-B2-3328547 includes a flow rate detecting chip, a circuit chip, leads and a support member. The flow rate detecting chip has a flow rate detecting portion including a heater (heat generating resistor) formed in a thin wall portion of a semiconductor substrate. The circuit chip has a circuit portion electrically connected to the flow rate detecting portion through connecting wires and processes an output signal of the flow rate detecting portion. The leads are electrically connected to the circuit portion through the connecting wires, and the support member is provided for mounting at least the flow rate detecting chip.
In a mounting state of the flow rate detecting chip onto the support member, a predetermined range including each connecting part of the connecting wires and the flow rate detecting portion and the circuit portion, each connecting part of the connecting wires and the circuit portion and the leads, and the circuit chip is integrally covered with a mold material, so as to expose one portion of the flow rate detecting portion including the heater to a measured fluid (e.g., air).
The support member has one end surface and two side surfaces which are bent in a perpendicular direction from a bottom surface portion where the flow rate detecting chip is arranged. The flow rate detecting chip is positioned by the one end surface and both side surfaces, and is arranged on the support member so as to close a cavity part of the lower portion of a thin film portion of a substrate of the flow rate detecting chip. Therefore, the cavity part of the lower portion of the thin wall portion of the flow rate detecting chip is blocked by the support member, and is not directly exposed to the measured fluid.
Accordingly, when a circumferential portion of the cavity part is fixed (e.g., adhered) to the support member so as to surround the cavity part of the substrate, it is difficult for the temperature of the fluid (air) sealed in the cavity part to follow a temperature change around the thermal-type flow rate sensor, and a measuring error is generated.
Further, if the flow rate detecting chip is partially fixed to the support member, the cavity part can communicate with the exterior through the clearance between the flow rate detecting chip and the support member. However, there is a predetermined clearance between each of the side surfaces (and one end surface) of the support member positioning the flow rate detecting chip, and the side surface of the flow rate detecting chip. Therefore, the mold material enters this clearance during the integral molding. In this case, the mold material may enter into the cavity part in accordance with the difference of an arrangement of the flow rate detecting chip, and the difference of formation of both the side surfaces (and one end surface) of the support member. Accordingly, the cavity part is blocked by this mold material, and the measuring error is generated.